The word "rieu" is a French term that refers to a small stream or a brook. Its spelling is derived from the French language and is pronounced as /rju/. The "r" sound is a voiced alveolar trill while the "j" sound is a voiced palatal approximant, which is similar to the "y" sound in English. The word is commonly used in geographical descriptions in French-speaking countries, and it can be found on maps or in tourism guides.